Reasons For Water Pump Mechanical Seal Leakage

May 20, 2025

Mechanical seals themselves are precision components with high requirements for design, machining, and assembly quality. When using mechanical seals, various factors related to the use of mechanical seals should be analyzed to ensure that they are suitable for the technical requirements and medium requirements of various pumps and have sufficient lubrication conditions, so as to ensure the long-term reliable operation of the seal.
Mechanical seal, also known as end face seal, has a pair of end faces perpendicular to the axis of rotation. Under the action of fluid pressure and compensating mechanical external elasticity, these end faces rely on the cooperation of auxiliary seals to maintain contact with the other end and slide relative to each other, thereby preventing fluid leakage.
1, Leakage caused by pressure
(1) Mechanical seal leakage caused by high pressure and pressure waves
Due to the excessive design of spring specific pressure and total specific pressure, as well as the pressure inside the sealing chamber exceeding 3MPa, the sealing end face will experience excessive specific pressure, making it difficult for liquid film to form. This will result in severe wear on the sealing end face, increased heat generation, and thermal deformation of the sealing surface.
Countermeasure:
When assembling mechanical seals, the compression of the spring must be carried out according to regulations, and there should be no excessive or insufficient phenomenon. Measures should be taken for mechanical seals under high pressure conditions. To ensure reasonable force distribution on the end face and minimize deformation, materials with high compressive strength such as hard alloys and ceramics can be used, and lubrication measures for cooling can be strengthened. Suitable transmission methods such as keys and pins can be selected.
(2) Mechanical seal leakage caused by vacuum operation
During the starting and stopping process of the pump, due to blockage of the pump inlet and the presence of gas in the pumped medium, negative pressure may occur in the sealing chamber. If there is negative pressure in the sealing chamber, it will cause dry friction on the sealing end face, and the built-in mechanical seal will produce air leakage (water) phenomenon. The difference between vacuum sealing and positive pressure sealing lies in the directional difference of the sealing object, and mechanical seals also have adaptability in one direction.
Countermeasure:
Adopting a dual end mechanical seal helps improve lubrication conditions and enhance sealing performance.
2, Leakage caused by the medium
(1) After disassembling the mechanical seals of most submersible sewage pumps, the auxiliary seals of the static and dynamic rings have no elasticity, and some have already rotted, causing a large amount of leakage and even grinding of the shaft of the seals. Due to the corrosive effect of high temperature and weak acids and bases in sewage on the static and dynamic ring auxiliary rubber seals, excessive mechanical leakage is caused. The material of the dynamic and static ring rubber seals is Nitrile-40, which is not resistant to high temperature and acid and alkali. When the sewage is acidic or alkaline, it is prone to corrosion.
Countermeasure:
For corrosive media, rubber parts should be made of fluororubber that is resistant to high temperatures, weak acids, and weak alkalis.
(2) Mechanical seal leakage caused by solid particle impurities, if solid particles enter the sealing end face, will scratch or accelerate the wear of the sealing end face. The accumulation speed of scale and oil on the surface of the shaft (sleeve) exceeds the wear speed of the friction pair, causing the dynamic ring to be unable to compensate for wear displacement. The operating life of hard to hard friction pairs is longer than that of hard to graphite friction pairs, because solid particles will be embedded in the sealing surface of the graphite sealing ring.
Countermeasure:
Mechanical seals of tungsten carbide friction pairs should be used in locations where solid particles are easily accessible.